Don't buy rechargeable small appliances (such as a dust-buster with a battery in it);
those usually want to plug in to 110V AC for long periods to recharge.
Get appliances that run directly off 12V DC, or some VDC that you can create
with a DC-DC converter from the main batteries.

"The nasty little secret to these over-priced and way-too-cute devices is that while they "carbonate" tap water,
they don't carbonate it very much. A liter of store-bought seltzer is pressurized to at least 95 lbs./sq. inch,
and can reach 120 lbs. or more on a hot day. Home devices deliver at most 45 lbs. or so, which is pretty weak.
... Saves money? Not really, just gives you less fizz for a bit less money. I buy food-grade CO2 in a refillable
5-lb. commercial tank for twenty bucks, fill a bunch of used plastic liter bottles to about 105-110 lbs.,
and each one costs me about FOURTEEN CENTS. And this is REAL soda."

"SodaStream is clearly concerned with product liability and injuries caused by their product.
Even when you're filling one of their bottles you can hear a lot of gas leaking out. I'm not at all
surprised if they only let you fill it up to half normal pressure."

"I've been keeping track of the output on a kitchen whiteboard, we've never gotten more than 30 liters from our cylinders,
and this is using a modest 3 "shots" (and short bursts and chilled water).
The Bed Bath and Beyond guy who loves to chat about his SodaStream whenever I'm in
for supplies begrudgingly conceded that he also gets nowhere near the promised 60 liters."

"I've tallied, and I get 60+ liters.
Some factors that increase the number of liters:
- using chilled water. I have 4 bottles, and when one gets used up, it gets refilled and put in the fridge rotation.
- using short bursts of fizz. If you hold the button down constantly until it buzzes, it uses much more CO2."

"The lack of waste plastic alone (recycling still costs resources) is a good reason to go for it, even if cost
for you ends up being roughly equal."